What's in the milk?

Have you ever taken care of someone’s animals or been to a farm that uses a different scoop for each grain or milk replacer they have? I know that I have and it even happens at my own farm. We use whatever is convenient and we make it work, right? A concern with this is that the scoop used to measure out milk replacer on one farm is not necessarily the same scoop as another farm down the road; they may be feeding different weights of milk replacer when they should be feeding the same.

When you look on any milk replacer tag it generally provides instructions for mixing based on weight. We do not often think about milk replacer as the amount of total energy or protein provided in a calf’s daily allotment but rather in the total volume that is given to each calf. Consequently, it is important to make sure we know how much each cup or scoop is measuring out so we are better able to target our calf raising goals.

A common goal in calf raising systems is to support good health and high average daily gains. Calves require energy and protein to support maintenance and growth. Maintenance in the calf includes basic functions of thermal regulation (in hot and cold conditions), immune responses, and stress responses. Requirements for maintenance of a 100-lb. calf, less than 21 days old, are 1.75 Mcal/d under thermoneutral conditions (59-77°F) using Cornell-Illinois modifications of NRC (2001). For example, if a 100-lb. calf under thermoneutral conditions was fed either a 20:20 milk replacer or a 24:20, how much would the calf have to consume just to meet maintenance requirements?

The amount of milk replacer that is needed might be more than you would expect. For the 20/20 milk replacer there would be 0.27 Mcal/L from protein and 0.12 Mcal/L from fat for a total of 0.39 Mcal/L provided, while the 24:20 milk replacer will provide 0.32 Mcal/L from protein and 0.12 Mcal/L from fat for a total of 0.44 Mcal/L. In order to meet the maintenance requirement on the 20:20 milk replacer the calf would have to consume 4.49 L (4.74 qt.) per day.

On the other hand, the same calf fed the 24:20 would only have to consume 3.98 L (4.21 qt.) per day to meet maintenance requirements under thermoneutral conditions. Once the requirement for maintenance has been met then additional Mcals can be partitioned toward growth. Therefore, a calf eating a similar volume of 24:20 milk replacer to a 20:20 milk replacer has an increased potential for gain because of the increased energy density of the milk replacer offered in a smaller volume of milk.

It is important to keep in mind that not all growth is the same on different milk replacers. Energy requirement is highest for maintenance but is greatly reduced once maintenance has been met. Alternatively, the protein requirement for maintenance is very low but increases for any additional growth. Consideration of feeding level is important when choosing a milk replacer. A typical 20:20 milk replacer for conventional feeding rates is not necessarily going to promote the same type of growth and composition at an accelerated feeding rate.

Fat deposition is different with different milk replacers and different feeding levels. As protein levels increase in the milk replacer, fat deposition decreases. This is true until about 28% crude protein (CP) which is similar to whole milk. Above this level, protein is wasted. At lower conventional levels (i.e. 8-10% of birth weight) where the goal is to get the calves off of milk and onto starter in the shortest amount of time, it is possible to overfeed protein because the limiting factor for growth becomes energy. Typically, accelerated feeding programs (i.e. 16-20% of body weight) will usually contain 24 to 26% CP as opposed to the 20% CP in the conventional feeding regimens because of the higher growth potential.

Overall, it is really beneficial to sit down and figure out how much protein and energy is being provided in the milk replacer that is fed to calves. Energy requirements are affected by thermoneutral conditions, immune status, and stress but also vary depending on size of the calf and body weight gain. Rethinking calf feeding in terms of energy density and total amount of energy provided in terms of Mcal and kg of dry matter of milk replacer provided as opposed to liters or quarts will help to target higher gains in calves. With these higher gains we should expect to see more productive animals in the future.